This is a Demo version
of the e-course. If you wish to take the e-course, you must acquire t he manual
of Geofísica
Práctica.

.

GEOPHYSICAL
NOTES- Introduction Course

2.
GRAVIMETRIC METHODS 2,1 Important definitions. * Gravimeter:
Used sensor to measure the gravitational field strenght point to point. It
is common that these apparatuses give a relative quantification of g (for example,
when comparing the elongación experienced by means of which it hangs a
mass pattern).* Gradiómetro of gravity: gravitational sensor
that measures the gradient of the gravitational field instead of its absolute
value. According to its direction, gradiómetro can measure the gradient
in X, and or Z (or combinations in diagonal). In simple terms, the gradient
corresponds to the fluctuation of the gravity by length unit.* Spheroid:
The normal spheroid corresponds to the form that would acquire our planet in the
case of being a doughy mass submissive the simultaneous action of the force of
gravity and the centrifugal force generated by the Earth spin.

2.2
TYPICAL GRAVITY SURVEY A) Phase of Land. To define a mesh and in each
node to measure the acceleration of gravity. B) Corrections. i) It derives
from the instrument: the gravimeter is not perfect, reason for which a mooring
station is used to quantify the drift of the zero (it is assumed linear).
II) Complementary angle of site: a hill increases the acceleration of gravity,
whereas a river basin makes diminish. All the data must take to flat topography
III) Other corrections: by latitude, of Faye, Bouguer, etc. C) Final map:
isoanómalas of gravity. The resulting map shows the variations undergone
by the acceleration of gravity like exclusive result of the different densities
from rocks. It can be advisable to make a statistical analysis of the gravity
and to show to the deviations respect to background (residual gravity).

2.3
Interpretation The interpretation of the topographical datas along with makes
use of the integral expression of the Law of Universal Gravitation the Gravitational
Law of Gaussian:

For example, the Gravitational Law of Gaussian
can be used to compare the topographical datas with the gravity generated by a
flat distribution of mass of thickness h and density uniforms r, when the measurements
are made to a distance r << h. In this case, as the system is equivalent
to an infinite plane, we will have g (r) will be constant, analogous to the result
that appears when using the Electrical Law of Gaussian for a condenser of parallel
flat plates.

In case of being in a land with
flat topography, we will have any anomaly of gravity will have to deviations of
the density of the subsoil respect to the density bases. In other
words, the gravitational anomalies are originated by variations in the distribution
of the mass density point to point (3D). On the other hand, if the topography
is complex, the gravity anomalies could be related or to the geometry of the land
and/or the distribution of densities, since g = g (density, position).

QUESTIONNAIRE
- Gravimetric Prospection

1) Select the correct alternative. The free air correction

a)
It reduces the value of the original data if these were moderate on the level
of the sea. b)
Differential g is derived from the expression (R+h) = g (R) + dg (h) c)
It is made discretizando the surface and seeing the effect of the topography on
each compartment.

2) Alternative selects the two correct. On the gravitational tension, we
can affirm that: